Generally, there are three representative methods for constructing an underground structure. First, in a down-top construction method, an earth retention wall is installed at a ground in which an underground structure will be built. A temporary horizontal strut is installed for dealing with an earth pressure of the earth retention wall, and a ground excavation work is performed, and a horizontal strut is installed for thereby completing an earth retention temporary construction. A main structure is installed in such a manner that a temporary structure is disassembled in a sequence from a deepest portion of an underground to the ground. Second, in a SPS (Strut as a Permanent System) construction method, an earth retention wall is installed at a ground in which an underground structure will be built, and a permanent vertical member is installed. An excavation work is performed, and a horizontal frame structure is installed. When an excavation is finished at the deepest portion of an underground, the works for a slab, concrete columns and walls are completed except for a vertical frame structure and a horizontal frame structure, and the construction is performed up to the aboveground portion. Third, in a top-down construction method, a slurry wall corresponding to an earth retention wall as well as a permanent wall structure is installed at a ground in which an underground structure will be installed, and a permanent vertical member is installed. When a horizontal frame structure and slab of a first floor of the ground are installed, an excavation is performed, and a main structure is installed. On the ground, the subsequent aboveground floor is built.
In more detail, in the above down-top construction method, a H-beam is installed at a surrounding portion of a ground in which an architecture will be built. An excavation is performed and at the same time a liner plate is installed between sheet piles, and then a girth is installed. Temporary horizontal struts are attached to the horizontal and vertical sides of a horizontal surface of the same for thereby supporting an earth pressure. In the above horizontal strut construction method, a H-beam is generally used for a temporary horizontal strut. A temporary vertical member called a center column for a connection with the H-beam is installed before a ground excavation so that the H-beam is not buckled by an earth pressure. During the excavation, the horizontal struts are installed in a two- or three-tier structure. It is connected with a corresponding center column at every floor.
The above SPS construction method is called a permanent trust construction method. In this method, an earth retention wall is constructed, and a steel member (PRD foundation), which is a permanent vertical member and is connected with a basic pile for dealing with a weight during an underground construction work period, is installed before an excavation construction. A horizontal frame structure is installed using a H-beam at each floor for thereby forming a horizontal strut and a permanent horizontal frame structure which substantially deal with the earth pressure. At this time, in the permanent horizontal frame structure, the sizes of the related members are determined so as to substantially deal with the earth pressure of the earth retention. The permanent horizontal frame structure should be connected with the previously installed permanent vertical members. In addition, it is installed up to the aboveground portion while completing the constructions at the slab, concrete columns and walls except for the vertical member and horizontal frame structure when the excavation is performed at the deepest portion of the underground floor. Here, when the underground mat slab is completed, the steel structure can be installed at the aboveground area.
In the top-down construction method, the foundation is formed along with the slurry wall construction. In the foundation construction work, a large size through hole is formed, and a H-beam is inserted for an underground vertical member (RCD foundation), and a basic concrete is cast at the basic portions, so that a structure of a horizontal frame structure of a first floor is formed. The upper and lower sides of the same are formed in the down-top construction method and the top-down construction method for thereby forming each floor.
However, the above-described down-top construction method, SPS construction method and top-down construction method have the following problems.
In the case of the down-top construction method, the earth retention wall should be disassembled at the construction step of the underground structure of the architecture. During the disassembling work, a sudden stress unbalance may occur at the earth retention wall. A certain crisis may occur during the disassembling work. The construction is not easy due to an interference with the related structures, so that a lot of damage may occur at the materials. The period of the disassembling work is disadvantageously extended. A certain deformation may occur at a surrounding ground area, so that a peripheral structure may be affected. Since the intervals of the center columns installed for preventing the horizontal struts from being buckled are narrow, the underground excavation work generally performed by the equipments is disadvantageously affected, and the construction period is extended by an interference of the temporary members during the framework.
In the case of the SPS construction method, since the piles (PRD foundation) referred to the permanent vertical members are installed before the underground is excavated, the intervals between the piles are narrow, so that the underground excavation work is difficult. As the permanent horizontal frame structure, the H-beam is connected with the corresponding piles for thereby obtaining the operation of the horizontal strut. At this time, the piles may have construction errors, so that it is needed to actually measure the H-beam and manufacture the same, whereby the construction period is disadvantageously extended. Furthermore, the connections with the steel piles are performed by a welding method, so that it is difficult to manage the quality. In addition, as the horizontal strut, the H-beam should be capable of dealing with a high earth pressure. However, since the H-beam has a strong axis and a weak axis, the size of the member is determined by the buckling of the weak axis, so that it is needed to separately manufacture the H-beam having a wider width, whereby the size of the member is uneconomically increased. So, the width of the H-beam as the horizontal frame structure increases, so that it is not easy install the steel of the pile and the matrix which are formed with a steel and concrete structure.
In the case of the top-down construction method, since the works of the slurry wall and RCD foundation are performed only with a large size equipment, a narrow area and a not-easy-to-enter area can not be worked using the above large size equipment. Since a pile (RCD foundation) referring to a permanent vertical member is first constructed before the underground is excavated, the excavation work can not be performed since the interval between the pile is too narrow. Since the construction is performed with the top-down construction method, it is impossible to connect the previously cast upper side concrete with the concrete which will be cast at the lower side of the same. In addition, since the steel of the horizontal frame structure formed with steel concrete is interfered with the H-beam of the previously installed vertical structure, the related connection and work are difficult, and the quality management is not easy. In addition, since the vertical member installed before the excavation has a construction error, a work for compensating the error is not easy.